Initial reports indicated one Afghan civilian was killed and at least six others were injured in the accident. There was no report of coalition casualties or of any casualties resulting from the subsequent unrest.

Later news reports say eight people were killed and more than 100 were injured, but military officials have yet to release an estimate beyond their initial report.

Coalition spokesman U.S. Army Col. Thomas Collins issued a statement that said a large cargo truck apparently experienced a mechanical failure and struck as many as 12 civilian vehicles at about 8 a.m.

U.S. soldiers at the scene immediately provided medical help to the injured, who were taken to local hospitals, Collins said, and Afghan security forces also responded.

When a crowd gathered at the scene and became hostile, a second convoy came to help, and both convoys moved out of the area with the damaged truck while Afghan security forces handled crowd control. Collins said a full investigation is under way, and that soldiers in at least one convoy vehicle may have fired warning shots over the crowd.

"We will determine the facts regarding the incident and cooperate fully with Afghan authorities," Collins said, noting that anyone entitled to compensation will receive it. "This was a tragic incident, and we deeply regret any deaths or injuries resulting from this incident," he said. "Although this incident is very regrettable, the coalition remains committed to working together with the people of Afghanistan to build a better future."

Appearing on CNN's "American Morning" today, Marine Gen. Peter Pace, chairman of the Joint Chiefs of Staff, said not enough information is available yet to come to any conclusions about the incident.

"Apparently there was a traffic accident of some kind," he told interviewer Miles O'Brien in an interview originally intended to focus on the nation's observance of Memorial Day. "As a result of that, a crowd gathered. I understand that some local police responded to the scene. After that it's a little bit sketchy as far as what happened. So I don't want to speculate. But there has been a problem there. We need to find out what happened."